: The goal of this project is to understand the molecular basis of GH action, using the serine protease inhibitor (Spi) 2 locus in the rats as a model system for the study of the nuclear events following GH signal transduction. Previous studies have demonstrated that Spi 2.1 contains a GH-response element (GHRE), which shows GH-specific binding requiring phosphorylation for activity. The applicant now proposes: 1) To isolate GH-inducible nuclear factor (GHINF) by GHRE affinity chromatography. Peptide sequences of the purified protein will be used to generate oligonucleotides for isolation of a cDNA for GHINF; 2) To characterize GHINF, in terms of similarity to other transcription factors, tissue specificity and ontogeny; 3) To examine the role of GHINF and its phosphorylation in GH action.